An image forming apparatus and a toner replenishment control method according to the present invention are configured such that a concentration of toner in a developer detected by a toner concentration detection sensor is measured and the measured toner concentration value is stored. These are configured such that regions of image data corresponding to an electrostatic latent image on an image bearing member to be developed by the developer are specified and an amount of toner to be consumed in the developer is predicted based on the image data of the specified regions, then a post-development concentration value of toner in the developer is estimated based on the measured toner concentration value and the predicted toner consumption amount, and control of replenishment of toner to the developer is carried out based on the estimated post-development toner concentration value and a toner setting concentration value that has been set in advance.